1. Field of the Invention
This invention relates to organopolysiloxane compositions having improved shelf stability and curing capability.
2. Prior Art
From the past, addition reaction between aliphatic unsaturated radicals and hydrosilyl radicals promoted by platinum group metal catalysts is utilized in a variety of applications. Inter alia, platinum compounds are used as catalytic compounds finding the most versatility in the field. Beside organic synthetic reaction such as synthesis of silalkane bonds, platinum compounds are also utilized in the silicone industry as means for crosslinking addition reaction type resins and rubbers. Applications include use as adhesives, coating agents, potting agents, gelling agents, and foaming agents, and extrusion, compression molding or injection molding of liquid or millable rubbers.
In the silicone industry, a fast-curing composition having a long shelf life is demanded from the working and operating standpoints. For compositions utilizing addition reaction as the crosslinking system, a number of proposals have been made on controlling agents for controlling the shelf life and pot life of platinum group catalysts. The controlling agents proposed heretofore include benzotriazole compounds (JP-B 25069/1965 corresponding to U.S. patent application Ser. No. 202,974 filed on Jun. 18, 1962), acetylene alcohol compounds (JP-B 31476/1969 corresponding to U.S. Pat. No. 3,445,420), vinyl-containing polysiloxane compounds (JP-B 10947/1973 corresponding to U.S. Pat. No. 3,699,073), hydroperoxides (JP-B 20340/1982 corresponding to U.S. Pat. No. 4,061,609), and amine compounds (JP-A 56563/1988 corresponding to EP 257,970). However, such chemical control has a limit in finding a compromise between pot life and curing rate, failing to meet the current market demand for prolonged storage and fast curing.
From the above standpoint, an attempt was made to enclose platinum group catalysts in thermoplastic resins or silicone resins so that the catalysts may be released to silicone compositions at elevated temperature causing the thermoplastic resins or silicone resins to be melted. This technology is disclosed in many patents, for example, JP-A 134786/1974, 37053/1983 corresponding to U.S. Pat. No. 4,481,341, 51140/1989 corresponding to U.S. Pat. Nos. 4,874,667 and 5,009,957, 9448/90 corresponding to U.S. Pat. No. 5,015,716, 14244/1990 corresponding to U.S. Pat. No. 5,017,654, 202193/1993 corresponding to EP 543,410, and 196921/1995 corresponding to EP 661,349.
These microcapsulation methods, however, have a likelihood of local curing because the platinum group metal catalyst is locally distributed in a silicone composition and in high concentrations.
To overcome this problem, JP-A 46962/1992 proposes to use acetylene alcohol as a reaction retarder, thereby preventing local curing reaction. This composition gives rise to several inconvenient problems when applied to a variety of areas.
For example, in the application as heat curing type silicone rubber adhesive wherein a tackifier component is added to these compositions, if the continuous manufacturing line is set at a relatively low temperature so that a certain time is required for the thermoplastic resin having the platinum group metal catalyst embedded therein to melt, then curing and bonding sometimes become incomplete in the manufacturing line. In another application, a hydroxyl source such as alcohol or water is blended in the composition whereby a foam is manufactured in a heating line. It is known that a minor amount of expansion by dehydrogenation reaction at the initial of reaction affords nuclei for expansion so that a satisfactory foam is obtained. However, the reaction retarder acts to suppress this initial expansion too, failing to form a satisfactory foam. In a further application wherein the compositions are used as millable type addition curing materials to mold cables and tubes, if the compositions are molded and vulcanized at a high speed, tack is left on the surface, failing to obtain molded products having a smooth surface.
Therefore, an object of the invention is to provide an organopolysiloxane composition having solved the aforementioned problems.